Sydney Airport IT glitch causes delays

Passengers at Sydney Airport have faced major delays after a "technical" issues halted security.

Order has been restored to Sydney Airport after a chaotic morning of queues and delays caused by an IT issue that affected security systems.

Long lines filled the international terminal and one of two domestic terminals early on Friday after an "underlying technology issue" was discovered before opening.

At 5am, the airport took the unusual step of advising passengers to avoid the T1 and T2 terminals until further notice. Qantas' domestic Terminal 3 was not affected.

Sydney Airport told frustrated passengers to check with their airlines for up to date information on flight delays.

A spokeswoman later said the systems had alerted management to an IT issue "well in advance" of the terminals opening.

"We identified that our systems, including our CCTV had been affected and we immediately worked with our technology providers to resolve the issue and ensure that security would not be compromised," they said in a statement.

"Our ongoing focus is working to strengthen and enhance our IT resilience."

The fault impacted passenger processing as a whole including some doors and alarms.

The problem was resolved by 9am, however airlines warned there would be knock-on delays throughout the day.

Jetstar's flight schedule was operating on time by midday but almost 30 flights were delayed before then.

The average delay was one hour with the longest wait nearly two and a half hours, a spokesman said.

Fewer than a dozen Virgin Australia flights were late by mid-afternoon while there were 10 Tiger Airways flights impacted overall.

In September last year, there was similar chaos at the airport caused by a radar failure on the first day of the NSW school holidays.

While the "air traffic control system failure" was resolved by 9am the same morning it interrupted flight patterns not only at the airport but across Australia.